In syntax, the distinction between domains and constituents (or phrases) has been proposed in order to account for certain syntactic phenomena. In phonetics and phonology, this distinction seems to held true in various work, the domain being related to a specific rule or process while the constituent being linked to the notions of head and hierarchical structure. However a closer look to the usage of these notions shows that the difference between these two types of entities is not well recognized in this field. In this paper we aim at clarifying the difference between both types of grouping in order to determine if both are necessary in order to account for specific phonetic and phonological phenomena.